A sealing material such as a gasket and a packing is used in a pipe flange or the like in various industries.
A sealing material is required to have the properties mentioned below. Since pipes are frequently exposed to high temperatures, it is required to have heat resistance sealing properties. Further, since a sealing material is cut off from a sheet at the time of production, it is required to have a strength enough to resist punching with a Thomson blade. Further, a sealing material is required to have a large compression amount in order to be in imitate contact with a flange having concave and convex on the surface thereof.
Various materials have been proposed as a sealing material. For example, as a sealing material used in a high temperature range, a sealing material made of expanded graphite is known (for example, see Patent Documents 1 to 4). A sealing material made of expanded graphite has sufficient elasticity and is excellent in heat resistance. However, since disappearance by oxidation of expanded graphite is accelerated in the presence of oxygen in a temperature range exceeding 500° C., it is difficult to maintain stable sealing properties for a long period of time.
Further, Patent Documents 5 to 7 disclose a sealing material made of mica. The sealing material disclosed in Patent Document 5 is a composite material (vortex) of swelling mica and fibers. Due to the use of fibers, it has poor sealing properties. Further, since it is prepared by papermaking, mica that is exfoliated is re-aggregated during drying, and thus only a dense thin film is formed, leading to a small compression amount. The sealing material disclosed in Patent Document 6 is a sheet (vortex) of swelling mica. Since only a high dense sheet can be produced, the sheet has a small compression amount. The sealing material disclosed in Patent Document 7 is a film of swelling mica, and has a small compression amount.
Patent Documents 8 to 10 each disclose a sealing material using clay. In the sealing material disclosed in Patent Document 8, since scale-like fillers are arranged in parallel, a dense film is formed. Therefore, only a sheet having a high density can be prepared. Due to a small compression amount thereof, concave and convex on the flange surface cannot be filled, and hence sealing properties in the plane direction are low.
In the sealing material in Patent Document 9, an organic foaming agent is incorporated into a clay film. An attempt is made to fill a gap with a flange (leakage along contact surface) by repulsive force generated by decomposition of an organic foaming agent. However, function is lowered under circumstances where heating or cooling is conducted, and hence, sealing properties are finally lowered. The sealing material in Patent Document 10 is a composite material of clay and fibers. As for this composite material, flexibility is imparted by fibers. However, this composite material had poor sealing properties.